Angry Car

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by fatdog, Jul 23, 2001.

  1. fatdog

    fatdog Registered Member

    Jun 1, 2001
    Likes Received:
    Soda Springs Idaho
    Ok, I know this isn't k5 related, but this forum is thriving with some very bright individuals, and I'm hoping someone can help me out. I also hope I'm not out of line here. This is just the most active forum, so I figured I'd have a better chance for help here.

    I've been fighting with my very angry 86 cavalier Z-24 2.8 mpfi for 3 days now, and I can't get the cooling fan to work. I have verified that the fan motor and the fuse is ok so those are not the problem. What I don't know enough about is the rest of the cooling circuit. What I do think I know is that the components involved are:

    1. The fan relay
    2. The air conditioning relay
    3. Three sensors/senders?
    4. A 20 amp fuse

    To explain further about the sensors/senders, I believe I have isolated the one on the side of the block near the firewall to be the temp. gauge sender. It appears to be ok because the guage works fine, and the guage works when the others are disconnected. That leaves the one in top of the thermostat housing (single wire), and the one in the intake manifold (double wire). I assume these are both temp. sensors of some type, but I don't know what each one is named specifically or how to test them. I have a Haynes manual, but it doesn't tell you what is what or give a specific wiring diagram for the 86 Z-24. If anybody can tell me what is what, and what part talks to what other part under what circumstances, I would be very thankful, I really suspect the car is running angrily because some part is lying to the ECM as to rather it is hot or cold or warm or cool and the computer is trying really hard to adjust for the faulty part. This obtuse crap drives me crazy sometimes, everything is so inter-related.

    As a side note, I have replaced both the relays, and the 2 top-side sensors, and the ECM (all one at a time) with parts from a parts car. Nothing changed. I don't really want to start replacing them with new relays and sensors (expensive) until I can hopefully isolate each item better. I just don't know enough.

    Oh yea, it is writing only a code 12 (normal), and a code 15 (cooling circuit).

    Thanks for any help.


    Self and Spouse Proclaimed GM Junkie
    She thinks I'm Sick and... She's Right
  2. HarryH3

    HarryH3 1 ton status Author

    May 31, 2000
    Likes Received:
    Georgetown, TX
    The gauge and the ECM don't read from the same sender. But I'm not sure where the sender for the ECM is located on that particular vehicle. [​IMG] Some GM engine temp senders are in the head while others are in the intake manifold. I'm pretty sure that the fan should run anytime the a/c is on (compressor running), regardless of engine temp.

    <font color=black>HarryH3 - '75 K5</font color=black>
    <a target="_blank" href=></a>
    It's a great day to be alive...
  3. DieselDan

    DieselDan 1/2 ton status

    Jan 27, 2001
    Likes Received:
    Code 15 means infinate resistence: either a disconnected temp sender, broken wire, or bad sender. If you disconnect the sender and ground it back into itself you should set a code 14: zero resistance. If that code doesn't set you've got a bad wire. The sensor reads less resistance as temp goes up. Hope this helps

    Real trucks don't have spark plugs!

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